If your microphone fails the breath test it probably has a capsule with build-up of contamination, typically dust and/or smoke (smog) deposits, sometimes incorrectly referred to as 'nicotine' residue. The moisture from close breath does combine with these deposits to provide an undesirable discharge path across the very high impedance capsule, thereby creating the typical frying and popping sound. If the noise diminishes once the humidity has dissipated, a (highly) experienced microphone technician may be able to restore proper operation by carefully cleaning the diaphragm(s) and surrounding high impedance areas.
If the noise is more permanent and often accompanied by drop-outs when the microphone subjected to high soundpressure, then the capsule is likely to exhibit other forms of deterioration. If it is an original M7 capsule with its gold sputtered PVC diaphragm air pollution is likely to have deteriorated the PVC material, which may have caused it to appear milky and brittle, perhaps even to a point where the gold film get partially detached. Attempts at cleaning such specimen are pointless, and the only proper remedy would be replacement of the capsule with the current K49 and the corresponding mounting hardware kit. IMHO an original Neumann K49 is much closer in acoustic and electronic properties to the M7 than any reskinned or cloned M7.
